Dolichol is a polyisoprenol lipid comprised of five-carbon isoprene units linked linearly in a head-to-tail fashion. Almost all eukaryotic membranes contain dolichol and its phosphorylated form is used in the N-glycosylation of proteins where it is used as an anchor for the N-glycan sugar to the ER membrane, and as an initiation point for the synthesis. Dolichol biosynthesis occurs on the cytoplasmic face of the ER membrane, which is where N-glycosylation occurs too, so is perfectly placed to serve as a substrate for this process. Dolichyl phosphate can be obtained either from direct phosphorylation of dolichol, formed in a series of reactions from mevalonate 5-pyrophosphate, or a salvage reaction by de-phosphorylation of dolichyl diphosphate, released at the end of N-glycan biosynthesis (Cantagrel & Lefeber 2011).